1. Field of the Invention
The present invention relates to an offset printing press having a wetting unit and an inking unit, the inking unit having an ink metering apparatus for the establishment of an ink profile, and wherein the inking unit and the wetting unit each have at least one applicator roller which can be moved into a contact position with a printing forme. As used herein, the term "printing forme" refers to an image bearing medium, the image on which is to be printed, e.g., a plate cylinder and/or a printing plate.
2. Background Information
On offset printing presses, it is often necessary to have a thin film of ink fed to the printing forme which has been wetted with a wetting agent. For this purpose, there may be provided an inking unit equipped with a number of rollers. The delivery of the wetting agent may be accomplished by means of a wetting unit, which also has an arrangement of rollers. Depending upon the image provided on the printing forme, it is desirable to establish an appropriate and corresponding ink distribution in a direction transverse to the direction of travel of the material to be printed through the offset printing press, to achieve a good printing result. Accordingly, the inking unit is preferably provided with an ink metering device which makes possible the zonal setting of an ink profile. The thickness of the ink layer in the individual zones is established as a function of the requirements for the individual zones. The ink is delivered by means of an ink ductor from an ink pan or reservoir. It is up to the printer to make the zonally required adjustment of the ink metering device as a function of the ink requirements of the image in question. This is done when setting up the offset printing press. Additionally, before the actual printing, a so-called "ink admission" (or "ink profile establishment") is conducted, in which the above-mentioned profiled ink film is built up inside the inking unit. In known prior art devices, during the ink profile establishment period, movable applicator rolls may assume a position where they are separated by some distance from the printing forme, so that there is not yet any inking of the image. The printing forme preferably consists of a plate cylinder, on the convex surface of which a printing plate bearing air image is mounted.
In addition to the ink distribution in the circumferential direction, the ink is also distributed laterally, to some degree, during the ink admission (or ink profile establishment), preferably, by laterally reciprocating (or oscillating) distribution rollers. Consequently, the ink remains pliant (or flexible) and is also uniformly distributed laterally. Undesirable accumulations of ink can also be avoided. However, the lateral distribution (or spreading by rubbing) during the ink profile establishment may, for example, lead to a situation where the ink profile constructed by the ink metering device is evened out to a certain extent once again, so that, in the start-up phase of the subsequent printing process, the lateral ink profile may not be available to the desired extent. Moreover, initially the ink distribution does not satisfactorily correspond to the image, which leads to the generation of waste sheets. Only when the appropriate printing run conditions are achieved, i.e., when an ink profile which properly corresponds to the image has been established, are good printing results achieved.
The problems described above also exist when a so-called "jam" occurs, i.e., a short interruption of the printing process, and also during a pause in the printing run to wash the blanket cylinder of the offset printing press, since, when the printing process is restarted, there will initially be a somewhat unsatisfactory ink profile.
German Published Patent Application No. 37 06 695 discloses a process for the generation of a defined ink distribution in the inking unit of rotary printing machines which is close to the ink profile required for the printing run, and in which, before the beginning of printing, first the ink profile present in the inking unit from the preceding printing job is removed, while the unit is rotating, by closing the ink metering elements and by the return feed into the ink reservoir of the amounts of ink present in the inking unit as a function of the profile, so that a basically constant thickness ink layer remains, the thickness of which is independent of the profile. Then the ink profile required for the subsequent printing job is generated in the inking unit by a zonal adjustment of the ink metering elements with a defined number of revolutions of the inking unit rollers.
Published German Patent Application No. 33 38 143 discloses a presetting of the inking unit. To generate a defined distribution of the ink in the inking unit which is close to that required for the printing run, a precisely measured quantity of ink is transported to the inking unit rollers before the beginning of printing by means of the vibrator rollers, so that a pre-determined distribution of ink layer thicknesses is established upon the rollers of the inking unit.
Published German Patent Application No. 15 61 100 discloses an inking unit for rotary printing presses which has controllable lifting means, to separate defined groups of rollers. These lifting means also move the applicator rollers which interact with the printing forme. When there is an interruption of the printing, the lifting means bring about a separation of certain groups of rollers, and also shut off the applicator rollers.